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Why is alternating current useful for gas-tungsten arc welding of aluminum?

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Welder in a blue uniform and protective helmet using shielded metal arc welding to join metal pieces, with bright sparks and smoke visible at the welding point. — welding Shielded metal arc welding.

In gas-tungsten arc welding (GTAW) of aluminum, the use of alternating current is essential for effective cleaning of the workpiece.

Aluminum naturally develops a very tenacious oxide film on its surface, which can hinder proper metal flow and the formation of a sound joint. When using the gas-tungsten arc process, alternating current enables the arc action to effectively remove this oxide layer, ensuring a cleaner and more successful weld.1